Satellites are important links for communication between stations at different locations throughout the world, particularly for mobile communication stations. For a satellite system to give worldwide coverage, a network or constellation of satellites is desirable.
Each satellite within such a satellite constellation has one or more directional antennas producing a coverage pattern on Earth referred to as the "footprint" of the satellite antenna. When multiple polar orbiting satellites are used, the satellites converge towards the poles and antenna footprints begin to overlap.
Where the antenna footprint is made up of separate "cells" in which individual communication is to take place, certain cells overlap. When cells from one satellite overlap cells from another satellite, the cells may be turned off as part of a cell management plan to prevent interference between cells of the same channels.
Individual satellites generally have limited energy resources. Typical energy resources aboard a satellite include batteries and solar cells to supply the power for satellite maintenance and communications. In a satellite communication system, the number of subscriber units in a particular geographic region requiring communication services may exceed the energy available to the satellite at that time. For example, this may occur in a satellite communication system where the satellites move with respect to the surface of the Earth when an individual satellite may, during some portion of its orbit, pass over high population density areas such as Europe, Japan or India where there is a high demand for communication services. The satellite may not have enough energy to provide communication services over these regions during peak hours. Furthermore, when the same satellite passes over several areas having high demand for communication services during its orbit, or passes over the same high demand area each orbit, the problem is worsened because the satellite may not be able to recharge its energy supply.
Thus what is needed is a method and apparatus for sharing the load created by high demand areas among other satellites in the communication system. What is further needed is a method and apparatus of transferring subscriber units from overloaded satellites to satellites not experiencing overload. What is further needed is a method and apparatus for distributing power loading move evenly among satellites in a satellite communication system.